The early darkness in winter is related to the distance from the direct point of the sun. In winter, it is far from the direct point of the sun, so the day is short and the night is long, and the night comes earlier. In summer, it is close to the direct point of the sun, so the day is long and the night is short, and the night comes later.
The direct point of the sun is the place where the incident angle of sunlight on the earth's surface (i.e. the solar altitude angle) is 90 degrees. It is the intersection of the connecting line between the earth's center and the sun's center and the earth's sphere.
The seasonal movement of the direct point of the sun causes changes in the length of day and night and the height of the noon sun. The northern hemisphere is the aphelion after July, with long days and short nights, while the southern hemisphere is on the contrary.
As for the long days in summer and the short days in winter, it is directly related to the latitude. The closer it is to the poles, the more obvious it is. It is not obvious near the equator, which is related to the sphere. In the Arctic Circle, from the spring equinox to the autumn equinox, it is always day without night. On the contrary, it is dark for half a year, because the sun shines for a long time in summer. （DongTianWeiShenMeTianHeiDeZao）